The openings in aircraft skins giving access to internal installations are usually referred to as manholes and their covers are commonly referred to as manhole covers or doors.
A manhole assembly for a fuel tank located in an aircraft wing must meet the following general requirements:                its size must be in accordance with accessibility requirements;        the manhole cover must be sealed for preventing fuel lass;        impact requirements must be met;        the assembly and disassembly of covers must be as quick and as easy as possible;        the covers must be changeable.        
For metallic wings a typical manhole assembly comprise a suitable dimensioned opening, an inner cover in the fuel tank and an outer cover in the wing surface. The inner and outer covers are joined by means of screws such that they secure the wing skin between them and the resulting pressure on the surrounding surface seals the whole cover through the action of sealing profiles. To maintain the aerodynamic continuity a rebate is machined on the skin edge so that the outer cover can be mounted over the skin rebated edge.
FIGS. 1 and 2 show a typical manhole assembly for a metallic wing lower skin. An inner cover 11 is located inside the fuel tank and an outer cover 13 is located on the wing surface. The inner and outer covers 11, 13 are joined by means of screws 15 clamping between them the metallic skin 17. Two sealing profiles 21, 23 are arranged at the ends of the inner and outer covers 11, 13 so that the screws pressure on the surrounding surface seals the whole cover. A rebate 25 is machined in the edge of the metallic skin 17 to mount the outer cover 13 over the skin for maintaining the aerodynamic continuity in the wing surface.
This prior art solution is not directly applicable to wings made of composite material, especially CFRP (Carbon Fiber Reinforced Plastic)—a recent event in the aeronautical industry—so that they need new manhole assemblies.
Patent applications WO 2009/003954 and WO 2009/083575 in the name of the applicant disclose two proposals in this respect.
WO 2009/003954 discloses a manhole assembly comprising the following elements: an outer and an inner cover; an adjusting washer between the inner cover and the skin; sealing profiles between the inner cover and the adjusting. washer and between the outer cover and the skin; a plate between the skin and the outer cover; the inner and outer cover being joined by means of screws such that they secure the wing skin between them.
WO 2009/083575 discloses a manhole assembly comprising an outer and inner cover, stringers attached to the skin whose edges are positioned so that the outer and inner covers are clamped on the foot of the stringer and are joined by means of screws and the outer cover is aligned with the skin for maintaining the aerodynamic continuity in the wing surface.
While these proposals solve the problem raised by aircraft wings of composite material for certain manholes, there is still a demand of a manhole assembly able to satisfy all the requirements of a manhole giving access to an installation placed inside an aircraft wing made of composite material.
The present invention is aimed at satisfying this demand.